I killed the boss and all enemies on the last floor and there is no way to get back down it seems.

After checking corners i found a hidden switch. Is this supposed to be invisible?

Good catch! It's certainly not intended and will be fixed in the next version.

The lever is only invisible if you never reload the game during that dungeon, which is why nobody has reported it until now I guess. Congrats on not save scumming :)

ah i said before in my comments the shortcut was removed but i did not know it was glitched thanks for heads up first comment.